1. Field of the Invention
The invention relates to an apparatus and method for detecting optical signals, and particularly to an apparatus and method for detecting two-dimension optical image signals.
2. Description of the Related Art
FIG. 1 shows a systematic view of a general apparatus for fluorescence signals detection. A sampling light beam L1′ passes an excitation filter or a monochromator 110. The filter or monochromator 110 lets the excitation laser L1 pass through and irradiate the labeled sample 120 in the testing zone. The labeled sample 120 is excitated to radiate fluorescence. The emission light L2 passes a second filter or a monochromator 112 where unneeded noise light is removed. Then, a monochromical emission is detected by a photodetector 130.
There are two technical manners for detecting fluorescence signals. The first manner is to apply laser as an excitation light and apply a photomultiplier tube (PMT) to detect the received signal and form a two-dimensional image. The second manner is to apply white light of mercury lamp or xenon lamp and to use a high-resolution camera, such as a CCD (charge-coupled device) camera, to take the fluorescence picture for further image analysis through an image analyzer.
The laser and photomultiplier tube detection system mainly follows the structure of an optical microscope. As shown in FIG. 2, a laser source 202 provides a laser beam to be separated by a dichroic mirror 210 and focused in the testing zone. The labeled sample 220 in the testing zone is excited to radiate fluorescence. The dichroic mirror 210 separates the excitation laser and the emission light into different paths. The light source is focused by lens into a spot. The size of the spot determines the resolution of the detection system. However, the size of the spot is restricted by the optical limitation of diffraction and the wavelength of the incident light. Furthermore, since the detection signal is processed with pixel of the focused spot, a precise moving device with displacement resolution higher than the optical resolution is required for obtaining a two-dimensional scanning. The precise device increases the hardware cost. The single point scanning also increases the imaging time and slows the operation.
There have been many prior devices for detecting fluorescence signals. For example, U.S. Pat. No. 5,719,391 discloses a fluorescence imaging system including an objective entrance pupil and a two-dimensional moving system. U.S. Pat. No. 5,780,857 discloses a scanning system with both laser and white light beams. U.S. Pat. Nos. 6,355,934, 6,471,916, 6,603,537, 6,628,385, 6,646,271 and 6,664,537 also disclose other derivative devices. Most of them are laser and photomultiplier tube systems using dichroic mirrors to separate the incidence excitation laser and the emission light. When omitting the dichroic mirror, the optical design may sacrifice the wholeness of entrance aperture of the received emission light.
The other detection devices with CCD cameras mainly use white light sources. However, the white light source occupies much space and generates a lot of heat that cause trouble and difficulty of system design. The system also requires two filters, in which one removes the excessive wavelength light in the incidence beam; the other removes the noise in the emission light. A dichroic mirror is also required to separate the incidence light and the emission light.
U.S. Pat. No. 6,630,063 discloses a fluorescence signal detection system applying capillary electrophoresis. The system also uses a laser beam refracted by lens and formed into scanning beams through a galvanometer. However, instead of two-dimensional scanning, it is only applicable to one-dimensional scanning.